What I'm trying to say is that public domain has issues within the international realm. With something like the BSD license you declare very explicitly what you allow and I believe (if I understand correctly, I am not a lawyer) according to the Berne Convention that those explicit declarations work in an international realm.
So if your product is never going to be used/sold/shipped out side of USA, England, and a few other countries Public Domain is alright. Otherwise you need to use something like Creative Commons Zero License or a BSD/MIT License.
The Berne Convention is much too old to specifically address the bare licenses used for open-source software. However one of the provisions of the convention is that any creative work is protected under copyright law without requiring explicit registration. This creates a problem for declaring something in the public domain since there is not really an established legal procedure for a copyright owner to waive or forfeit the exclusive rights which have been automatically granted to them.
